1. Field of the Invention
The present invention generally relates to a light emission control technology and, more particularly, to a light emission control apparatus and a light emission control method for controlling the quantity of light emission by adjusting a current for driving a light emitting element.
2. Description of the Related Art
The light-emitting diode (LED) element is used for a variety of purposes in battery-driven portable equipment such as a portable telephone and a personal data assistant. For example, LED elements are used to provide backlight of a liquid crystal display or a flash light of a charge-coupled device (CCD) camera. LED elements producing difference colors may be operated to blink so as to provide illumination.
Characteristically, the quantity of light emitted by an LED element is increased in proportion to a current. The light emission efficiency depends on the temperature of the LED element. As the element temperature is increased as a result of an increase in the current, the light emission efficiency abruptly drops due to heat generated. When the element temperature goes higher than specifications, optical output is prevented from being increased even if the current is increased further. The driving current of some ultra-high luminance LED elements exceeds 100 mA so that the optical output drops significantly due to thermal resistance. In order to overcome this problem, study is being undertaken to produce an LED element of high-intensity light emission with special provisions for heat dissipation.
As described, it is necessary to take into account the problem with heat in controlling the light mission of an LED element. Japanese Laid-Open Patent Application 2002-64223 discloses a driving circuit which is provided with a temperature detecting means for detecting the temperature of a semiconductor light-emitting element such as an LED and which uses an output of the temperature detecting means to control a driving current of the light-emitting element.
The driving circuit of the related art requires a temperature sensor for detecting the ambient temperature of a light-emitting element so that the cost of manufacturing the driving circuit is increased.
Related Art List
                JPA laid open 2002-64223.        